Mr Macron spoke on the phone with the PM this morning about the "progress of the investigation".

A statement reads: "Since the beginning of the week, the United Kingdom has kept France closely informed of the evidence gathered by British investigators and evidence of Russia's responsibility in the attack.

"France agrees with the United Kingdom that there is no other plausible explanation and reiterates its solidarity with its ally."

It goes on: "The President of the Republic and the Prime Minister condemn all use of chemical weapons.

"They recall the importance of full compliance with international conventions and their commitment to the fight against impunity for the use of chemical weapons.

"Our two countries will continue their cooperation in this area, in particular the OPCW (Organisation for the Prohibition of Chemical Weapons), the United Nations and NATO, in conjunction with our partners in the European Union.